If carbon-14 has a half-life or 5,730 years, how much of a 50g sample of carbon-14 would be left after 2 half-lives?

After 1st half life the remaining carbon is 25 g as 50/2= 25g showing that 25g decay and 25g will left.

After second half life it is 25/2=12.5 shows that

After two half lives there will be 12.5g of C-14 is left from 50g of sample

1) H2O

Explanation:

this is because there is a bond between two nonmetals, Hydrogen and oxygen,  so the bond is covalent. all the other are bonds between a metal and nonmetal so it is ionic.